The present invention relates to a projector for projecting an image produced by a liquid crystal display.
Portable equipment that must display information to a user, such as laptop computers, have in the past advantageously employed large liquid crystal display (LCD) panels as the primary information display device. Large LCD panels provide significant advantages over other large display devices in terms of volume occupied per unit of display area and in terms of power consumption to operate the display itself. Large LCD panels, however, require illumination and therefore typically require high power consuming cold cathode lamps along with complex light guides to provide reasonably uniform illumination.
It has been suggested that significant power and cost saving can be realized in a next generation laptop computer by replacing the large direct-viewing LCD panel with a virtual image display. Through the use of optical elements, a virtual image display projects a magnified virtual image of a small LCD panel directly into the user's eye. Because of the inherent optical efficiency of a virtual image display of this type, the entire image can be illuminated by a single light emitting diode consuming 5-10 milliwatts of power versus the 1-2 watts of power consumed by conventional large LCD backlighting apparatus. Moreover, because the virtual image display employs relatively easily manufactured small LCD panels, significant cost savings are realizable over the use of the technically challenging large direct-viewing LCD panels. The small size of the virtual image display also allows for a highly portable apparatus. Finally, because a virtual image display can only be seen by a single user, use of a virtual image display also precludes eavesdropping by others when the user is working in a public place, such as on an airplane.
One potentially significant disadvantage, however, is that because the virtual image display can only be seen by one person at a time, a computer or other apparatus equipped with such a display would not be capable of displaying information to two or more persons needing to see the information simultaneously. In such cases, a conventional direct-viewing display would be needed. Moreover, some users may find it uncomfortable to wear or hold the virtual image display in front of the eye. Accordingly, except where the benefits of power savings outweigh the discomfort of holding or wearing a virtual display, visor such a user may prefer a direct-viewing display even for individual use. Although a conventional laptop docking station with a separate cathode ray tube (CRT) display or large panel LCD could be utilized, such an approach would necessarily entail a complete duplicate display device with commensurate added cost.
What is needed is a docking station capable of converting an image produced by a virtual image display into a real image without duplicating the LCD panels, drive electronics and other active components already incorporated into the virtual image display.